JP3926928B2 - Printing apparatus, printing method, and recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes a head that includes inks having different densities for at least one hue and that can form two or more types of dots having different ink amounts for each of the inks. The present invention relates to a printing apparatus, a printing method, and a recording medium.
[0002]
[Prior art]
2. Description of the Related Art In recent years, color printers that eject several colors of ink from a head have become widespread as computer output devices, and are widely used for printing images processed by a computer or the like in multiple colors and multiple gradations. With respect to such a printing apparatus, a printing apparatus and a printing method using dark and light inks have been proposed for the purpose of further improving the printing quality in a low image density region, that is, a so-called highlight portion (for example, Japanese Patent Application No. Hei 8- 209232). This is intended to realize printing with excellent gradation expression by preparing inks with high density and low density for the same color and controlling the ejection of both inks.
[0003]
In addition, as another means for expressing multi-gradation, there is also a printing apparatus capable of printing by changing the density per unit area in multiple stages by forming two types of dots having different ink densities and ink amounts. It has been proposed (for example, JP-A-59-201864). In this case, one pixel is composed of 4 dots, and by changing the appearance frequency of pixels with high and low density, it is possible to print an image with multiple levels of density.
[0004]
On the other hand, in a printer that ejects ink to form dots, the amount of ink per unit area, that is, the ink duty, is controlled so as not to exceed a predetermined value corresponding to the printing paper. If the ink is ejected exceeding this value, the paper is easily torn, and bleeding or the like occurs, thereby impairing the image quality of the printed image.
[0005]
[Problems to be solved by the invention]
However, in a printing apparatus capable of forming two types of dots having different ink densities and ink amounts, no consideration has been given to the ink duty. In the first place, in such a printing apparatus, both are formed in a predetermined pattern according to the gradation of the input pixel, and how to cope with the ink duty limit has not been studied. It was. In addition, no consideration has been given to controlling not only the ink duty but also the amount of ink used for dot formation as a whole, such as to cope with the problem of how to use ink with different densities in a balanced manner.
[0006]
The present invention has been made in view of the above problems, and in a printing apparatus, for example, when there is a restriction on the ink duty, and when it is necessary to control the amount of ink used for forming dots, the ink density and the ink amount are provided. An object is to provide a technique for effectively utilizing two or more types of dots having different sizes.
[0007]
[Means for solving the problems and their functions and effects]
In order to solve at least a part of the above problems, the present invention employs the following means.
The printing apparatus of the present invention includes:
A printing apparatus capable of printing an image by forming a plurality of dots on a print medium,
Input means for inputting image data for each pixel constituting the image;
A head comprising two or more types of inks having different densities for at least one hue and capable of forming two or more types of dots having different ink amounts for each ink;
An ink amount expected value setting means for setting an expected value of the ink amount to be used for forming a dot for each pixel based on the image data for the inks having different densities;
Based on the set expected ink amount, each of the inks having different densities can be selected by selecting which of the two or more types of dots should be formed, including non-forming dots. Multi-value conversion means for performing value conversion;
Dot forming means for forming the selected dots,
The multi-value conversion means includes
Type-specific expected value setting means for setting a type-specific expected value for each type of dot that can be formed by the head based on the ink amount expected value determined by the ink amount expected value determining means When,
The gist of the present invention is a multivalued means having an error diffusion method and means for judging the presence / absence of dot formation based on the set expected value for each type of dot.
[0008]
The printing method of the present invention includes:
Forming a plurality of dots on a print medium using a head that includes two or more types of inks having different densities for at least one hue and capable of forming two or more types of dots having different ink amounts for each ink. A printing method for printing an image by:
For each pixel that makes up the image, input the image data,
For the ink of different density, set an expected value of the amount of ink to be used for dot formation for each pixel based on the image data,
Based on the set expected ink amount, each of the inks having different densities can be selected by selecting which of the two or more types of dots should be formed, including non-forming dots. Valuation,
A printing method for forming the selected dots;
The multi-value conversion is
Based on the expected amount of ink determined by the expected amount of ink determining means, an expected value for each type, which is an expected value for the amount of ink for each type of dot that can be formed by the head, is set.
The gist of the present invention is to use an error diffusion method for each dot type to determine the presence or absence of dot formation based on the set type-specific expected value.
[0009]
In such a printing apparatus and printing method, with respect to two or more types of inks having different densities provided for at least one hue, first, an expected amount of ink to be used for forming dots should be set for each pixel and then formed. Select the dot type. By adopting such means, the amount of ink provided for dot formation can be controlled appropriately.
In addition, since the above multi-value conversion means sets the expected value of the ink amount for each type of dot and controls the generation for each type of dot so that there is no error in the entire image, Are relatively uniformly distributed in the image. In general, a dot having a larger amount of ink is more conspicuous, and if such a dot is locally formed, the image quality is greatly impaired. According to the multi-value quantization means, dots with a large amount of ink are evenly distributed, so that a good image quality in which the dots are not noticeable can be obtained.
[0010]
Here, the expected value of the ink amount means an ideal ink amount that is ejected to each pixel in order to express the gradation value of the image data. The amount of ink that can be used for dot formation by the head of the printing apparatus of the present invention is actually limited to several predetermined types. However, the expected value of the ink amount is not limited to such several types and is predetermined. Can take continuous values within the range. Generally, an expected value is used as a term indicating probability, but in this specification, there is no such meaning, and it is used as a term meaning a value expected to be discharged to each pixel.
[0011]
The expected amount of ink does not need to use the exact amount of ink necessary to express the gradation value of the image data, but may include the characteristics of the dot forming means that actually ejects ink and other factors. It can be determined in consideration. The expected value of the ink amount may be set larger or smaller than the strict ink amount necessary for expressing the gradation value. Of course, it is also possible to set a large value for the expected ink amount for a certain gradation value and a small value for another gradation value.
[0012]
In the above printing apparatus,
The image data is data including a gradation value for at least one color component in a color space;
The ink amount expected value setting means includes:
Expected value storage means for storing the expected value of the ink amount as a table corresponding to combinations of gradation values of a plurality of color components in the color space;
By referring to a table stored in the expected value storage unit based on the input image data, a unit for setting an expected value of the ink amount for each pixel may be provided.
[0013]
The expected value of the amount of ink ejected for each pixel can be determined according to the combination of gradation values of a plurality of color components in the color space. According to the above means, the expected value of the ink amount can be set for each pixel based on the table thus determined.
[0014]
In the printing apparatus,
The table stored in the expected value storage means sets the expected value of the ink amount to the expected value of the ink amount of the other colors regardless of whether the hue is the same as the expected value of each ink to be set. It is desirable that the table is a table that stores the values determined in association with each other in correspondence with combinations of gradation values of a plurality of color components in the color space.
[0015]
In the table stored in the expected value storage means, the expected value of the ink amount of each color is determined in relation to the expected value of the ink amount of other colors, thereby improving the image quality while controlling the overall ink amount Etc. can be achieved. For example, consider a case where there is an upper limit for the amount of ink ejected per unit area. In the case where the printing apparatus prints a predetermined density using two types of light and dark inks for cyan, when the expected value of the ink amount of other hues is small, there is room for the upper limit value. It is possible to set so that a large amount of light ink in which dots are relatively inconspicuous is used. On the other hand, when the amount of ink of other hues is large, there is no room for the predetermined amount, so that it is possible to use a relatively small amount of dark ink having a high density for cyan.
[0016]
As the multi-value conversion means in the printing apparatus, various methods can be adopted,
It may be a dither method or an error diffusion method.
[0017]
When the types of dots that can be formed by the printing apparatus are limited, the expected value of the ink amount set in advance and the ink amount actually used for dot formation do not always match. An error occurs in the ink amount for each pixel. According to the printing apparatus including the above-described units, even if an error occurs in each pixel, it is possible to perform multi-value processing so that the error is reduced as a whole image. Furthermore, the dither method can perform multi-value processing at high speed, and the error diffusion method can appropriately suppress errors and obtain good image quality.
[0020]
In the printing apparatus,
The two or more types of dots formed for the same hue by the head may include two or more types of dots that have substantially the same average density per unit area when dots are formed with at least one recording density. desirable.
[0021]
When there are two or more types of dots having the same average density per unit area, there is a degree of freedom that any dot can be used in the density at which an image is recorded using these dots. As a result, it is possible to appropriately use both in accordance with various conditions such as improving the image quality while controlling the ink amount. In general, the relationship between the average density per unit area and the dot recording density varies depending on the type of dot. In order to obtain the effects described above in the present invention, it is sufficient that at least one density is present such that the average density is substantially the same when two or more types of dots are formed at the same density and compared.
[0022]
In each printing apparatus described above,
The ink amount expected value setting means is a range in which the total amount of ink used for forming dots per unit area does not exceed a predetermined amount determined according to the printing medium regardless of whether or not the hue is the same. It may be a means for setting an expected value of the ink amount.
[0023]
@ According to such a printing apparatus, the total amount of ink provided per unit area can be controlled so as not to exceed a predetermined amount determined according to the printing medium. In general, there is an upper limit on the amount of ink that can be absorbed by the print medium. When printing is performed with an ink amount exceeding the upper limit, the print medium is easily broken and the image quality is deteriorated due to blurring. In the printing apparatus, the amount of ink can be controlled so as not to exceed the upper limit, and thus various problems can be avoided.
[0024]
The predetermined amount determined according to the print medium is comprehensively determined based on various factors such as blur characteristics of the print medium, ink drying time, image quality of the printed image, and deformation of the print medium due to ink absorption. The ink amount is set as a preferable value above. Of course, such a predetermined amount is not uniquely determined depending on the printing medium, but also varies depending on the printing speed, the color of the ink used for printing, and the like. By considering such an upper limit, the expected value of the ink amount is set to a value different from an ideal value that should be set from the viewpoint of obtaining good image quality when there is no restriction on the ink amount. . From this point of view, as an aspect in which the expected amount of ink is set in consideration of a predetermined amount, for example, when the printing medium is so-called plain paper and dedicated for low penetration of ink manufactured for the purpose of high-quality printing There is a case where the expected value of the ink amount corresponding to an image having the same gradation value is changed with paper.
[0025]
The predetermined amount is the total amount of ink provided per unit area, and may exceed the predetermined amount locally. For example, even if a certain pixel exceeds the predetermined amount, the amount of ink ejected in the vicinity thereof is small, and the expected value of the ink amount is determined so as not to exceed the predetermined amount as a whole. I just need it.
[0026]
In the above printing apparatus, as a head capable of forming inks having different densities or different amounts of ink, ink particles are ejected by pressure applied to the ink by applying voltage to the electrostrictive element provided in the ink passage. A mechanism is conceivable. In addition, a mechanism that ejects ink particles by the pressure applied to the ink in the ink path by bubbles generated by energization of the heating element provided in the ink path forms dots with different concentrations of ink, It is also possible to form dots of different amounts. According to these configurations, it is easy to make the ink particles fine and control the ink amount appropriately, and it is also easy to prepare a large number of ejection nozzles on the head. In the case where a large number of nozzles are provided, a plurality of ink particle ejection nozzles can be arranged along the transport direction of the printed paper for each color and each density of ink. By preparing a plurality of nozzles, the printing speed can be improved.
[0027]
Since the printing apparatus of the present invention described above can also be configured by realizing some of the functions by a computer, the present invention can also take the form of a recording medium recording such a program. .
[0028]
The first recording medium of the present invention is
A recording medium in which a program for printing an image by forming a plurality of dots on a printing medium is recorded so as to be readable by a computer,
A function for setting an expected value of the amount of ink to be used for forming dots for each pixel based on image data for inks having different densities prepared for at least one hue;
For inks having different densities, multi-value conversion is performed by selecting which of the two or more types of dots should be formed, including the non-formation of dots, based on the set expected value of the ink amount. Functions to do,
It is a recording medium on which a program for realizing the function of forming the selected dots by a computer is recorded.
[0029]
The second recording medium of the present invention is
A recording medium on which data used for printing an image by forming a plurality of dots on a printing medium is recorded so as to be readable by a computer,
For inks of different densities prepared for at least one hue, the total amount of ink provided for the formation of dots per unit area regardless of whether the hue is the same or not is determined according to the print medium A memory in which data relating to the expected value of the amount of ink used to form dots for each pixel, which is determined within a range not exceeding 1, is recorded corresponding to a combination of gradation values for a plurality of color components in the color space. It is a medium.
[0030]
By executing the program recorded in the first recording medium on the computer, the printing apparatus of the present invention described above can be realized. When such a program is separately prepared, the printing apparatus of the present invention can be realized by using data recorded on the second recording medium by the computer.
[0031]
Storage media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed materials printed with codes such as bar codes, and computer internal storage devices (memory such as RAM and ROM). ) And external storage devices can be used. Moreover, the aspect as a program supply apparatus which supplies the computer program which implement | achieves the function of each process or each means of said invention to a computer via a communication path is also included.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples.
(1) Device configuration
FIG. 2 shows a schematic structure of the printer 22 of the present invention, and FIG. 1 shows a configuration of a color image processing system as an example system using the printer 22 of the present invention. In order to clarify the function of the printer 22, first, an outline of the color image processing system will be described with reference to FIG. This color image processing system includes a scanner 12, a personal computer 90, and a color printer 22. The personal computer 90 includes an input unit 92 including a color display 21, a keyboard, a mouse, and the like. The scanner 12 reads color image data from a color original, and supplies original color image data ORG composed of three color components of red (R), green (G), and blue (B) to the computer 90.
[0033]
The computer 90 includes a CPU, RAM, ROM, etc. (not shown), and an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and the final color image data FNL is output from the application program 95 via these drivers. An application program 95 that performs image retouching or the like reads an image from the scanner 12 and displays the image on the CRT display 21 via the video driver 91 while performing predetermined processing on the image. When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives image information from the application program 95, and this signal FNL (here, cyan, light cyan, magenta, light magenta) that the printer 22 can print. , Yellow, and black). In the example shown in FIG. 1, the printer driver 96 includes a rasterizer 97 that converts color image data handled by the application program 95 into image data in dot units (hereinafter referred to as pixels), and image data in dot units. The ink amount expected value setting module 98 and the ink amount expectation value setting module 98 for setting the expectation of the ink discharge amount for each color in consideration of the ink color used by the printer 22 and the color development characteristics are referred to. An expected value table CT and a halftone module 99 that generates so-called halftone image information expressing density in a certain area depending on the presence or absence of dot formation for each pixel based on an expected value of the set ink amount Is provided. The printer 22 receives the printable signal FNL and records image information on a recording sheet.
[0034]
Next, a schematic configuration of the printer 22 will be described with reference to FIG. As shown in the figure, the printer 22 includes a mechanism for transporting the paper P by the paper feed motor 23, a mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 by the carriage motor 24, and a print head mounted on the carriage 31. And a control circuit 40 that controls the exchange of signals with the paper feed motor 23, the carriage motor 24, the print head 28, and the operation panel 32. Yes.
[0035]
The carriage 31 of the printer 22 is supplied with black ink (Bk) cartridge 71 and inks of six colors, cyan (C1), light cyan (C2), magenta (M1), light magenta (M2), and yellow (Y). The stored color ink cartridge 72 can be mounted. For two colors, cyan and magenta, two types of light and dark inks are provided. The density of these inks will be described later. A total of six ink ejection heads 61 to 66 are formed on the print head 28 below the carriage 31. An inlet pipe 67 (which guides ink from the ink tank to the color heads) is provided at the bottom of the carriage 31. (See FIG. 3). When a black (Bk) ink cartridge 71 and a color ink cartridge 72 are mounted on the carriage 31 from above, an introduction tube 67 is inserted into a connection hole provided in each cartridge, and the ejection heads 61 to 66 are ejected from each ink cartridge. Ink can be supplied to the printer.
[0036]
A mechanism for ejecting ink will be briefly described. FIG. 3 is an explanatory diagram showing a schematic configuration inside the ink ejection head 28. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out via the introduction pipe 67 using the capillary phenomenon as shown in FIG. The print head 28 is guided to each color head 61 to 66. When the ink cartridge is first installed, an operation of sucking ink to the respective color heads 61 to 66 is performed by a dedicated pump. In this embodiment, a pump for sucking and a cap for covering the print head 28 at the time of sucking are performed. The illustration and description of such a configuration is omitted.
[0037]
As will be described later, the heads 61 to 66 for each color are provided with 32 nozzles Nz for each color (see FIG. 6), and each of the nozzles is one of electrostrictive elements and is responsive. An excellent piezo element PE is arranged. FIG. 4 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown in the drawing, the piezo element PE is installed at a position in contact with the ink passage 68 that guides ink to the nozzle Nz. As is well known, the piezo element PE is an element that transforms electro-mechanical energy at a very high speed because the crystal structure is distorted by application of a voltage. In the present embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE extends for the voltage application time as shown in the lower part of FIG. One side wall of 68 is deformed. As a result, the volume of the ink passage 68 contracts according to the expansion of the piezo element PE, and the ink corresponding to the contraction becomes particles Ip and is ejected from the tip of the nozzle Nz at high speed. Printing is performed by the ink particles Ip soaking into the paper P mounted on the platen 26.
[0038]
The printer 22 having the hardware configuration described above rotates the platen 26 and other rollers by the paper feed motor 23 to convey the paper P (hereinafter referred to as sub-scanning), and reciprocates the carriage 31 by the carriage motor 24. Simultaneously (hereinafter referred to as main scanning), the piezo elements PE of the color heads 61 to 66 of the print head 28 are driven to discharge the inks of the respective colors to form dots and form a multicolor image on the paper P. .
[0039]
The mechanism for transporting the paper P includes a gear train (not shown) that transmits the rotation of the paper feed motor 23 not only to the platen 26 but also to the paper transport rollers. Further, the mechanism for reciprocating the carriage 31 has an endless drive belt 36 stretched between the carriage motor 24 and a slide shaft 34 that is mounted in parallel with the axis of the platen 26 and slidably holds the carriage 31. And a position detection sensor 39 for detecting the origin position of the carriage 31.
[0040]
5 and 6 are explanatory views showing the arrangement of the inkjet nozzles Nz in the ink ejection heads 61 to 66. FIG. The printer 22 of this embodiment can form three types of dots with different ink amounts for each color. If the dots are formed in a circle, dots having three types of large, medium, and small dot diameters are formed. Hereinafter, “dots having different ink amounts” and “dots having different dot diameters” are used synonymously in this sense.
[0041]
In order to form dots with different dot diameters, for example, as shown in FIG. 5, a method of providing nozzles with different diameters for each color is also conceivable, but in this embodiment, all have the same diameter as shown in FIG. Using nozzles, dots having different dot diameters are formed by the control described later. The arrangement of these nozzles consists of six sets of nozzle arrays that eject ink for each color, and 32 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. Note that the 32 nozzles Nz included in each nozzle array need not be arranged in a staggered manner, and may be arranged on a straight line. However, when arranged in a zigzag pattern as shown in FIG. 6, there is an advantage that the nozzle pitch k can be easily set small.
[0042]
Here, the principle of forming three types of dots having different dot diameters using a head having a fixed nozzle diameter will be described. FIG. 7 is an explanatory diagram showing the relationship between the drive waveform of the nozzle Nz and the ejected ink Ip when the ink is ejected. A drive waveform indicated by a broken line in FIG. 7 is a waveform when a normal dot is ejected. Once a negative voltage is applied to the piezo element PE in the interval d2, the piezo element PE is deformed in the direction in which the cross-sectional area of the ink passage 68 is increased, contrary to the case described with reference to FIG. 7, the ink interface Me called meniscus is indented inside the nozzle Nz. On the other hand, when a negative voltage is suddenly applied as shown in the section d2 using the driving waveform shown by the solid line in FIG. 7, the meniscus is indented greatly inward as compared with the state A as shown in the state a. Next, when the voltage applied to the piezo element PE is positive (section d3), ink is ejected based on the principle described above with reference to FIG. At this time, a large ink droplet is ejected from the state where the meniscus is not dented so much (state A), as shown in state B and state C, and from the state where the meniscus is greatly recessed (state a), state b and Small ink droplets are ejected as shown in state c.
[0043]
As described above, the dot diameter can be changed according to the rate of change when the drive voltage is made negative (sections d1 and d2). In the present embodiment, based on such a relationship between the drive waveform and the dot diameter, a drive waveform for forming a small dot having a small dot diameter and a medium dot having the second dot diameter are formed. Two types of drive waveforms are prepared. FIG. 8 shows drive waveforms used in this embodiment. The drive waveform W1 is a waveform for forming a small dot, and the drive waveform W2 is a waveform for forming a medium dot. By using both appropriately, it is possible to form two types of dots having a small and medium dot diameter from a nozzle Nz having a constant nozzle diameter.
[0044]
Moreover, a large dot can be formed by forming a dot using both of the drive waveforms W1 and W2 of FIG. This state is shown in the lower part of FIG. The lower part of FIG. 8 shows a state from the ejection of the small and medium dot ink droplets IPs and IPm ejected from the nozzle to the paper P. When two types of small, medium, and small dots are formed using the drive waveform of FIG. 8, the ink droplet IP is ejected vigorously because the medium dot has a larger amount of change in the piezo element PE. Due to such a difference in the flying speed of ink, when the carriage 31 moves in the main scanning direction, small dots are ejected first, and then medium dots are ejected. If the timing is adjusted according to the distance between the carriage 31 and the paper P, both ink droplets can reach the paper P at the same timing. In this embodiment, the largest dot having the largest dot diameter is formed from the two types of drive waveforms shown in FIG.
[0045]
The internal configuration of the control circuit 40 of the printer 22 will be described, and a method for driving the head 28 including the plurality of nozzles Nz shown in FIG. 6 using the above-described drive waveform will be described. FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG. 9, the control circuit 40 includes a CPU 41, a PROM 42, a RAM 43, a PC interface 44 for exchanging data with the computer 90, a paper feed motor 23, a carriage motor 24, an operation panel 32, and the like. A peripheral input / output unit (PIO) 45 for exchanging signals with the timer, a timer 46 for measuring time, a transfer buffer 47 for outputting dot on / off signals to the heads 61 to 66, and the like. These elements and circuits are connected to each other via a bus 48. The control circuit 40 is also provided with a transmitter 51 that outputs a drive waveform (see FIG. 8) at a predetermined frequency, and a distributor 55 that distributes the output from the transmitter 51 to the heads 61 to 66 at a predetermined timing. ing. The control circuit 40 receives the dot data processed by the computer 90, temporarily stores it in the RAM 43, and outputs it to the transfer buffer 47 at a predetermined timing. Therefore, image processing for forming a multi-tone image is not performed on the printer 22 side. The control circuit 40 simply controls on / off in units of dots, that is, whether or not to form dots.
[0046]
A mode in which the control circuit 40 outputs signals to the heads 61 to 66 will be described. FIG. 10 is an explanatory diagram showing connection of one nozzle row of the heads 61 to 66 as an example. As shown in the figure, one nozzle row of the heads 61 to 66 is interposed in a circuit having the transfer buffer 47 as the source side and the distribution output device 55 as the sink side. Each of the piezo elements PE constituting the nozzle array has one electrode connected to each output terminal of the transfer buffer 47 and the other connected to the output terminal of the distribution output unit 55 all at once. Since the drive waveform of the transmitter 51 is output from the distribution output device 55, when the CPU 41 determines ON / OFF for each nozzle and outputs a signal to each terminal of the transfer buffer 47, according to the drive waveform, Only the piezoelectric element PE that has received the ON signal from the transfer buffer 47 side is driven. As a result, the ink particles Ip are simultaneously ejected from the nozzles of the piezo element PE that has received the ON signal from the transfer buffer 47.
[0047]
As shown in FIG. 8, the drive waveform is such that the small dot waveform W1 and the medium dot n waveform W2 are alternately output. Therefore, when it is desired to form a small dot for a certain pixel, the small dot drive is performed. An ON signal may be sent to the nozzle row in synchronization with the waveform W1, and an OFF signal may be sent to the nozzle row in synchronization with the medium dot drive waveform W2. In the case of forming medium dots, on the contrary, an OFF signal is sent to the nozzle row in synchronization with the drive waveform W1, and an ON signal is sent to the nozzle row in synchronization with the drive waveform W2. Further, when a large dot is formed, an on signal may be sent in synchronization with both drive waveforms. By doing so, the printer 22 of this embodiment can form dots with large, medium and small dot diameters during one main scan with each nozzle array.
[0048]
However, three types of drive waveforms for forming large, medium, and small dots and three transmitters that output the respective drive waveforms are prepared, and the drive waveforms are selectively used according to the dot diameter to be formed. By doing so, you may make it form the dot which consists of each diameter. Further, the dot diameters need not be limited to the three types of large, medium, and small, and the number of types of drive waveforms may be increased so that more dot diameters can be output. It is good also as what uses only a kind.
[0049]
As shown in FIG. 6, since the heads 61 to 66 are arranged along the transport direction of the carriage 31, the timing at which each nozzle row reaches the same position with respect to the paper P is shifted. Accordingly, the CPU 41 outputs the dot ON / OFF signal via the transfer buffer 47 at a necessary timing after taking into account the positional deviation of the nozzles of the heads 61 to 66, and sets the dots of the respective colors. Forming. Further, as shown in FIG. 6, the output of on / off signals is controlled in consideration of the fact that each of the heads 61 to 66 has nozzles formed in two rows.
[0050]
In this embodiment, large, medium, and small dots (hereinafter referred to as light large dots, light medium dots, and light small dots) formed with low density light ink and large, medium, and small dots formed with high density dark ink, respectively. , Small dots (hereinafter referred to as dark dots, dark medium dots, and dark dots), which are different in density in six stages. On the other hand, for example, a person who sets the dark dot and the light large dot so as to have substantially the same density may be used. The fact that the two densities are substantially the same means that the average density per unit area when both are recorded at a certain recording density is substantially the same. With this setting, the number of gradations that can be expressed for each pixel is reduced, but the degree of freedom in selecting dark and light dots can be increased.
[0051]
In this embodiment, as described above, the printer 22 having the head for ejecting ink using the piezo element PE is used. However, a printer for ejecting ink by other methods may be used. For example, the present invention may be applied to a printer of a type in which electricity is supplied to a heater arranged in the ink passage and ink is ejected by bubbles generated in the ink passage. In such a printer, since the dots having different dot diameters can be formed by changing the energization time and the energization area to the heater, the present invention can be applied.
[0052]
(2) Dot generation processing routine
Next, a dot generation processing routine in the embodiment according to the present invention will be described. FIG. 11 shows the flow of a dot generation processing routine according to the first embodiment. This routine is a part of the processing in the halftone module 99 of the printer driver 96, and is a routine executed by the CPU of the computer 90 in this embodiment.
[0053]
When the dot generation processing routine is executed, the CPU inputs pixel gradation data (step S100). The data input here is image data composed of RGB after converting a color image into image data in dot units. In this embodiment, the pixel gradation data is given by 8 bits, and the gradation value ranges from 0 to 255 for each hue.
[0054]
Next, the CPU executes a process of determining an expected value of the ink amount to be ejected for the six colors of ink provided in the printer 22 (step S200). The expected value of the ink amount is set so that a color corresponding to the input image data is printed. At this time, the expected value of the ink amount of each color is determined so that the sum of the ink amounts of all six colors does not exceed the amount of ink that can be ejected per unit area of the printing paper (hereinafter referred to as ink duty). For cyan and magenta having two types of light and dark inks, in order to express the density given as image data, how much light and dark ink is used is set. Since various processing contents can be considered for this process, the cases will be described later.
[0055]
When the expected value of the ink amount to be ejected for each color is determined by the process of step S200, the CPU performs a process of setting the diameter of the dot to be formed based on the expected value of the ink amount (step S300). Since various processing contents can be considered for this processing, the cases will be described later.
[0056]
According to the above processing, according to the input image data, the ink diameter of each color is determined while keeping the ink duty limit, and the dot diameter is determined within a range not exceeding the ink amount. In the printed image, the ink duty limit is always observed.
[0057]
(3) Each color ejection ink amount expected value determination processing
Various modes are conceivable for the process for setting the expected value of the amount of ink ejected per unit area while keeping the ink duty limit for each color. Below, the process which consists of three aspects is sequentially demonstrated as an example of this process.
[0058]
First, the expected ink discharge amount determination process for each color as the first mode will be described with reference to the flowchart of FIG. When this routine is started, the CPU refers to the expected value table IT for each color to determine the expected value of the ink amount to be ejected (step S210). Here, what is called each color means the color of each ink and does not mean the hue. That is, in this routine, the cyan ink and the light cyan ink are processed separately, and the expected value of the ink amount is set for each.
[0059]
Here, the expected value table IT will be described. FIG. 13 and FIG. 14 show examples of expected value tables in the present embodiment. FIG. 13 is a table that gives the expected value of cyan ink according to the red and green gradation values of the input pixel gradation data. FIG. 14 is a table that gives the expected value of light cyan ink in the same format. For the sake of illustration, blue data is shown as being constant at a certain value. Actually, there are 256 graphs in FIG. 13 corresponding to the change in blue. Although shown in the form of graphs in FIGS. 13 and 14, in practice, data corresponding to all combinations (256 × 256 × 256 points) of blue, red, and green gradation values are in the form of a table. And stored in the ROM of the computer 90. The expected values of the inks shown in FIGS. 13 and 14 are not only the cyan ink and the light cyan ink but also the expected values of the magenta ink and other inks, and the total expected value is the limit of the ink duty of the printing paper. It is set not to exceed. Tables similar to those in FIGS. 13 and 14 are set for other inks.
[0060]
In step S210, the CPU reads the value corresponding to the image data from each of the tables, and sets the expected value of the ink ejection amount. After performing this processing for all colors (step S215), the process returns from the ejection ink amount expected value determination processing routine to the dot generation processing routine.
[0061]
According to the ejection amount expected value determination process, since the data of the expected value of the ejection ink amount is stored in the form of a table according to all combinations of each gradation data, the processing content is very simple, There is an advantage that it can be processed at high speed. In addition, there is an advantage that it can be easily applied even if the data of the expected value of the ink ejection amount is very nonlinear data.
[0062]
In the above description, when the processing is completed for each pixel, it has been described that the expected ejection amount determination process for each color is temporarily ended. However, the result of each pixel is stored in the memory, and each raster or the entire image is stored. It is good also as what performs an iterative process.
[0063]
In the above description, the processing is performed for each color. However, instead of the table prepared for each color, the expected value of the ink amount of each ink is stored as a set corresponding to the input data. By using this table, it is possible to set all the ink amounts at once.
[0064]
Next, each color ejection ink amount expected value determination process as the second mode will be described with reference to the flowchart of FIG. This mode is a method of determining the expected value of the ink discharge amount by reducing the number of data points in the expected value table IT shown in FIGS. 13 and 14 and appropriately performing an interpolation calculation. That is, in the second mode, the expected value table IT (FIGS. 13 and 14) that gives the expected value of the ink ejection amount does not store data for all combinations of blue, red, and green. The table stores data only for specific grid points.
[0065]
When the ejection ink amount expected value determination processing routine is started, the CPU selects a grid in which pixel gradation data exists (step S220). In the second mode, since the expected value table IT exists only for a specific grid point, the expected value data of the corresponding ink discharge amount may not exist depending on the pixel gradation data. The CPU selects which grid the pixel gradation data belongs to in order to perform an interpolation operation later.
[0066]
The lattice will be specifically described with reference to FIG. FIG. 16 is an explanatory diagram showing lattice points based on red and green data. For convenience of illustration, the case where blue has a certain value is shown. As already described, red data and green data are data that can take 256 gradation values from 0 to 255. In the plane of FIG. 16 in which blue is fixed to a certain value, pixels represented by a combination of both. There will be 256 × 256 types of data. In the first aspect, expected value data of the amount of ink to be ejected is stored for each of these points.
[0067]
On the other hand, in the second mode, as shown in FIG. 16, assuming a grid in which each gradation value 0 to 255 is equally divided into 8 for red data and green data, only grid points that are intersection points are assumed. The ink discharge amount expected value data is stored. Therefore, for example, the gradation value 63 is a value that can be taken as pixel data, but the expected value table IT does not have data corresponding thereto.
[0068]
In the present embodiment, as shown in FIG. 16, a grid point exists for each gradation value 32. These grid points are indicated by numbers 0, 1, 2,... 8 in order from the gradation value 0 (hereinafter, these numbers are referred to as grid point numbers). In the present embodiment, it is possible to determine which lattice the pixel gradation data belongs to by dividing each value of red data and green data by 32 and rounding up after the decimal point. For example, with respect to the gradation value 63, the result of the above calculation is the value 2, so it is determined that it exists in the grid between the grid point number 2 and the grid point number 3. In this embodiment, it is assumed that the lattice points are arranged at equal intervals, but the lattice points do not necessarily have to be arranged at equal intervals, and the division of red data and green data does not have to match. . A grid having pixel gradation data is selected for blue by the same method as that for selecting grids for red and green. By such processing, one rectangular parallelepiped having pixel gradation data is selected in a three-dimensional color space of blue, red, and green.
[0069]
After the grid to which the pixel gradation data belongs is thus selected, the ink amount expected value data is interpolated using the grid points constituting the grid (step S230). There are eight lattice points constituting the lattice. Since various methods are known for performing so-called linear interpolation on the data of such eight lattice points, detailed description is omitted here.
[0070]
The expected value of the ink amount to be ejected is obtained by interpolation calculation, and after executing this process for all colors (step S235), the process returns from the expected ink amount determination process routine to the dot generation process routine.
[0071]
According to such an aspect, an interpolation operation is required, so that the processing speed is inferior to that of the first aspect, but the data amount of the ink amount table IT can be reduced, so that the memory amount can be saved. There is.
[0072]
The process of setting the expected value of ink amount is a so-called color in that a set of data relating to each color such as cyan and light cyan is given based on a set of input data having three elements of blue, red and green. This process is similar to the correction process. Therefore, various techniques used in the color correction process can be applied in addition to the two modes described above. For example, in each of the above embodiments, a method using the expected value table IT that stores the expected value data of the ink amount is employed. However, when the expected value data is expressed as a function of the pixel gradation data, such a method is used. The expected value of the ink amount may be obtained based on the function.
[0073]
(4) Dot diameter setting process
Various modes are also conceivable for the dot diameter setting process for setting the diameter of the dot to be formed based on the expected value of the ink quantity obtained by the ink quantity expected value determination process described above. Hereinafter, three modes will be sequentially described as examples of the dot diameter setting process. Each of the following modes can be adopted without depending on which mode described above is applied as the ink amount expected value determination process. When the dot diameter is continuously changed, it is possible to set the dot diameter so that the expected value of the set ink amount matches the actually ejected ink amount. Only limited types of dot diameters can be formed. Therefore, when viewed for each pixel, an error occurs between the set expected ink amount and the ejected ink amount. In the present embodiment, the dot diameter to be formed for each pixel is selected so that the error is suppressed to be small in the entire printed image by various processes described below.
[0074]
The first dot diameter setting process will be described based on the flowchart shown in FIG. Here, a case where the expected value of the ink amount for cyan ink is set to the value Cd will be described as an example.
[0075]
When the dot diameter setting process is started, the CPU inputs ink amount expected value data Cd (step S302). This data is expected value data of the ink amount to be ejected per unit area obtained in the ink amount expected value determination process described above.
[0076]
Next, it is determined whether or not the ink amount expected value data Cd is smaller than a predetermined value Vs (step S304). The predetermined value Vs is a value indicating the amount of ink assumed to be ejected by a dot having the smallest dot diameter (hereinafter referred to as a small dot) (hereinafter referred to as a small dot ink amount). When the ink amount expected value data Cd is smaller than the small dot ink amount Vs, it is determined whether or not the ink amount expected value data Cd is greater than or equal to the threshold ths in order to determine whether or not to form a small dot. (Step S306). If it is smaller than the threshold value ths, it is determined that small dots are not formed, and a value of 0 is substituted into the dot diameter setting data Cdr (step S308). If it is larger than the threshold value ths, it is determined that a small dot should be formed, and a value Vs corresponding to the small dot ink amount is substituted into the dot diameter setting data Cdr (step S310).
[0077]
Note that the predetermined value Vs used in step S304 and the value Vs substituted for the dot diameter setting data Cdr are different values as long as they are determined based on the amount of ink ejected to form a small dot. It may be used. For example, a value that is actually used to form a dot, that is, a value that is substituted into the dot diameter setting data Cdr may be smaller than the value that is used as a criterion in step S304. In this way, even when the amount of ink actually ejected varies from nozzle to nozzle, the ink duty limit can be maintained.
[0078]
Here, the threshold value ths will be described. In this embodiment, a threshold matrix of distributed dither is used for setting the threshold. The concept of the threshold in the dither method will be described later. In this example, a systematic dither method was applied using a global matrix (blue noise matrix) of about 64 × 64 in particular. In this dither matrix, the threshold value is determined so that there is no large bias in the appearance of the threshold value (0 to 255) in any 16 × 16 region within the 64 × 64 matrix.
[0079]
In step S306, since the expected ink amount data Cd can only take values 0 to Vs, the threshold ths is obtained by normalizing the above-described dither matrix to the range of values 0 to Vs. That is, each value th of the above-mentioned dither matrix is converted using the following equation so that the threshold value ths matches this range.
ths = th × Vs / 255
[0080]
Here, the concept of the dither method will be described with reference to FIG. Here, Vs is described as a value 64. As shown in FIG. 18, it is assumed that the ink amount expected value data is equal to or lower than Vs in an area composed of 4 × 4 pixels. The threshold value ths in such a region is given by a table obtained by normalizing a dither matrix, and threshold values having values from 0 to 64 appear as shown in FIG. By comparing this threshold value and the ink amount expected value data for each pixel, ON / OFF of the small dot is determined as shown in FIG. As described above, the dither matrix is set so that the threshold values appear evenly. Accordingly, if small dots are turned on / off by such a method, an error occurs between the expected ink amount and the actually ejected ink amount for each pixel, but when viewed as the entire image. This error is reduced.
[0081]
If it is determined in step S304 that the expected ink amount Cd is greater than the small dot ink amount Vs, the ink amount expected value Cd is the next dot having the second dot diameter (hereinafter referred to as a medium dot). It is determined whether or not the ink amount Vm is assumed to be ejected (step S312). If it is smaller than the ink amount Vm, it is determined whether or not the ink amount expected value data Cd is larger than a predetermined threshold value thm (step S314). If it is smaller than the threshold value thm, it is not a medium dot but a small dot. The value Vs corresponding to the small dot ink amount is substituted into the dot diameter setting data Cdr (step S316). If it is larger than the threshold value ths, it is determined that a medium dot should be formed, and a value Vm corresponding to the medium dot ink amount is substituted into the dot diameter setting data Cdr (step S318). If the dot is smaller than the threshold value thm, the medium dot is not formed and the small dot is formed. If the medium dot is not formed, the error with respect to the expected ink amount Cd increases. This is because it is not preferable.
[0082]
The threshold value thm is determined by the dither matrix described above. In step S314, since the ink amount expected value data takes values Vs to Vm, the threshold value thm is normalized to match this range by using the following equation for each value th of the dither matrix.
thm = th × (Vm−Vs) / 255 + Vs
[0083]
In step S312, when it is determined that the expected ink amount Cd is larger than the medium dot ink amount Vm, it is determined whether a dot having the largest dot diameter (hereinafter referred to as a large dot) is on or off. It is determined whether or not the ink amount expected value data Cd is larger than a predetermined threshold value thl (step S320). If the ink amount expected value data Cd is smaller than the threshold value thl, it is determined that medium dots are formed instead of large dots. A value Vm corresponding to the medium dot ink amount is substituted into the diameter setting data Cdr (step S322). If it is larger than the threshold value thl, it is determined that a large dot should be formed, and a value Vl corresponding to the large dot ink amount is substituted into the dot diameter setting data Cdr (step S324).
[0084]
The threshold value thl is determined by the dither matrix described above. In step S320, since the expected ink amount data Cd takes values Vm to Vl, the threshold value thl is normalized to match this range by using the following equation for each value th of the dither matrix.
thm = th × (Vl−Vm) / 255 + Vm
[0085]
Thus, the dot diameter of the dots to be formed, including the presence or absence of dot formation, was set. The CPU executes this process for all colors (step S326) and ends the dot diameter setting process.
[0086]
According to this aspect, it is possible to appropriately form dots having respective dot diameters according to the set expected ink amount. As described above, by using a dither matrix, it is possible to avoid the occurrence of locally biased dots, and when viewed as an entire image, the amount of ink ejected relative to the expected value of the set ink amount. The error can be kept small.
[0087]
In the above description, the thresholds ths, thsm, and thl are determined based on the dither matrix. However, these thresholds may be determined by generating a random number for each pixel.
[0088]
Next, the dot diameter setting process of the second aspect will be described based on the flowchart of FIG. When the dot diameter setting process is started, the CPU inputs the expected ink amount data Cd (step S340), and adds correction errors Cdx from the neighboring pixels that have already been processed to create correction data Cdx (step S342). . In the second mode, error diffusion processing is employed as will be described later as processing for bringing the actually ejected ink amount closer to the set expected ink amount Cd. In the error diffusion process, an error in the ink amount generated for the processed pixel is distributed in advance to the pixels around the pixel with a predetermined weight, so that in step S342, the corresponding error is read and this error is now read. This is reflected in the pixels to be printed. FIG. 20 exemplifies how much weight is distributed to which pixels in the periphery with respect to the pixel PP of interest by which weighting. With respect to the pixel PP of interest, the density error is a predetermined weight (1/4, 1/8) for several pixels in the scanning direction of the carriage 31 and several adjacent pixels on the rear side in the transport direction of the paper P. , 1/16). The error diffusion process will be described in detail later.
[0089]
The CPU compares the correction data Cdx with predetermined threshold values Th1 to Th3 (steps S344 to 352). The predetermined threshold has a relationship of Th1 <Th2 <Th3. If the correction data Cdx is smaller than the threshold value Th1 (step S344), it is determined that no dot is formed, and a value 0 is substituted into data Cdr for setting the dot diameter (step S346). If the correction data Cdx is larger than the threshold th1 and smaller than the threshold th2 (step S348), it is determined that a small dot should be formed, and the value Vs is substituted into the dot diameter data Cdr (step S350). If the correction data Cdx is larger than the threshold th2 and smaller than the threshold th3 (step S352), it is determined that a medium dot should be formed, and the value Vm is substituted into the dot diameter data Cdr (step S354). If the correction data Cdx is larger than the threshold th3 (step S352), it is determined that a large dot should be formed, and the value Vl is substituted into the dot diameter data Cdr (step S356).
[0090]
As described above, it is set what kind of dots should be formed including the case where dots are not formed. Next, the CPU executes error calculation and error diffusion processing based on such settings (step S358). The error here refers to an error between the correction data Cdx corrected in step S342 and the actually ejected ink amount Cdr. This error is caused by the fact that the correction data Cdx can take a value of, for example, 0 to 255 continuously, whereas the actually ejected ink amount Cdr can take only a certain discrete value. For example, if the ink amount Vl of a large dot is 255, if a large dot is formed even though the correction data Cdx is 199, there is an ink amount error of 255-199 = 56. It is happening. This means that the amount of ejected ink is too large compared to the set ink amount. Since the amount of ink ejected is given by Cdr, the error ERR is obtained by ERR = Cdx−Cdr.
[0091]
The error diffusion refers to a process of diffusing the error thus obtained by adding a predetermined weight (see FIG. 20) to pixels around the pixel PP currently being processed. Since the error should be diffused to the unprocessed pixels, as shown in FIG. 20, the error is diffused only to the pixels arranged in the carriage scanning direction and the paper conveyance direction. Based on the above example, if the error is 56, 14 corresponding to 1/4 of the error 56 is diffused to the pixel P1 adjacent to the currently processed pixel PP. This error is reflected in step S342 when the pixel P1 is processed next. For example, if the data of the pixel P1 is a value 214, the diffused error 14 is subtracted therefrom to set the correction data to a value 200. By repeatedly executing such processing, each pixel includes an ink amount error, but the image as a whole is printed with an ink amount corresponding to the set ink amount expected value data. With this process, the dot diameter including the presence / absence of dot formation is set for all the colors (step S360), and this routine is temporarily terminated.
[0092]
If such processing is used, the processing amount is inferior in terms of processing speed because it is complicated compared to the first embodiment, but the ink amount error can be reliably eliminated, and a better image can be obtained. . Note that the weight values shown in FIG. 20 are merely examples, and other weight values may be used.
[0093]
Next, the dot diameter setting process according to the third mode will be described based on the flowchart of FIG. In the third mode, the error diffusion method is used in the same manner as in the second mode. In the second mode, the dots having the respective diameters are integrally processed. This embodiment is different in that dots having respective diameters are individually processed.
[0094]
When the dot diameter setting process is started, the CPU inputs the expected ink amount data Cd (step S370), and sets the expected ink amount for each dot diameter based on the data Cd (step S372). The expected ink amount for each dot diameter is determined based on a preset table. An example of such a table is shown in FIG. FIG. 22 is a representation in which the expected value of the ink amount of the dot having each dot diameter is replaced with the occurrence rate of each dot in accordance with the expected ink amount value Cd. The expected value of the ink amount is obtained by multiplying the ink amount ejected to form each dot by the dot generation rate. When the expected ink amount Cd is relatively small, for example, in the section Cd1, it means that the ink amount should be formed with only small dots. Accordingly, in the section Cd1, the expected value of the ink amount for medium dots and large dots is both 0. In the other sections (sections Cd2, Cd3, Cd4), the expected value of the ink amount corresponding to each dot diameter is similarly set. The expected ink amount for each of the small dots, medium dots, and large dots set in this way is Cds, Cdm, and Cdl.
[0095]
Next, the CPU creates correction data Cdsx, Cdmx, Cdlx by adding diffusion errors from neighboring pixels that have already been processed (step S374). Cdsx, Cdmx, and Cdlx are the results obtained by individually correcting the ink amounts Cds, Cdm, and Cdl of small dots, medium dots, and large dots by diffusion errors. Thus, in the third mode, processing is executed independently for each dot diameter.
[0096]
Next, the CPU substitutes correction data Cdsx for error Errs for small dots, correction data Cdmx for error Errm for medium dots, and correction data Cdlx for error Errl for large dots as temporary error setting values (step S376). ). This value is a value corresponding to an error when a dot having each dot diameter is not formed in the following processing.
[0097]
After the error is temporarily set in this manner, it is first determined whether or not the large dot correction data Cdlx is larger than a predetermined threshold value thr (step S378), and if it is larger than the threshold value thr, a large dot should be formed. And the value Vl is substituted into the dot diameter data Cdr, and the error Errl corresponding to the large dot is changed to the difference between the correction data Cdlx and the value Vl (step S380).
[0098]
When the large dot correction data Cdlx is smaller than the threshold value thr, that is, when a large dot is not formed, it is determined whether or not the medium dot correction data Cdmx is larger than the predetermined threshold value thr (step S382). If it is larger than thr, it is determined that a medium dot is to be formed, and the value Vm is substituted into the dot diameter data Cdr, and the error Errm corresponding to the medium dot is changed to the difference between the correction data Cdmx and the value Vm. (Step S384).
[0099]
When the medium dot correction data Cdmx is smaller than the threshold value thr, that is, when the medium dot is not formed, it is determined whether or not the small dot correction data Cdsx is larger than the predetermined threshold value thr (step S386). If it is larger than thr, it is determined that a small dot should be formed, and the value Vs is substituted into the dot diameter data Cdr, and the error Errs corresponding to the small dot is changed to the difference between the correction data Cdsx and the value Vs. (Step S388). When the small dot correction data Cdsx is smaller than the threshold value thr, no dot is formed.
[0100]
With the above processing, it is set which dot should be formed including the presence or absence of dot formation. In addition, an error was set according to the result. For the dots that are not formed, the error data temporarily set in step S376 remains as it is.
[0101]
Next, the CPU performs a process of diffusing this error (step S390). The weight for diffusing the error is the same value as the weight used in the second mode. In the third aspect, error diffusion is performed independently for each of the errors Errs, Errm, and Errl corresponding to each dot diameter. The above processing is performed for all the colors (step S392), and this routine is once ended.
[0102]
According to such processing, as in the second aspect, errors can be appropriately eliminated in the entire image, and a good image can be obtained. In the third aspect, a better image than in the second aspect can be obtained for the following reason. That is, in the second mode, since the dots having all the diameters are integrally subjected to error diffusion processing, there is a possibility that dots having a large dot diameter are locally biased. In the case where such a bias occurs particularly in high-density ink, the graininess becomes conspicuous and the image quality is lowered. On the other hand, in the third mode, as a result of performing error diffusion processing for each dot diameter, dots having each dot diameter are dispersed throughout the image, so that the above-described bias is less likely to occur and is favorable. An image can be obtained.
[0103]
Based on the result of the dot generation processing routine described above, the CPU executes processing for the printer 22 to form each dot. Since various processes are known for this process depending on the configuration of the printer 22, the description based on the flowchart is omitted here. In this embodiment, as described above, large, medium, and small dots can be arbitrarily formed from individual nozzles during one main scan of the carriage 31, so what is the dot diameter to be formed by the above-described processing? Even if it is set, it can be realized relatively easily.
[0104]
On the other hand, the above-described dot diameter setting process is performed by a printer that selectively uses, for example, three types of drive waveforms prepared for large, medium, and small dots, that is, dots that can be formed at one time by a set of nozzle arrays The present invention can also be applied to a printer having a constant diameter. In such a printer, dots having different dot diameters are mixedly formed by scanning using a well-known overlap type dot recording method. An example of such scanning will be described below.
[0105]
FIG. 23 schematically shows a scanning example in the case where large and small dots are mixed in a 6 × 6 area using a head with 6 nozzles. In FIG. 23, the state of ink ejection corresponding to the number of head scans is shown on the left side, and the state of dots formed on the right side is shown. The number given to each dot corresponds to the scanning order of the head. As shown in FIG. 23, in the first main scanning, large dots are formed every other dot in the main scanning direction using the lower half nozzles of the head. Next, after the sheet is conveyed by 3 dots in the sub-scanning direction, small dots are formed every other dot in the main scanning direction using all the nozzles. Then, after the sheet is further conveyed in the sub-scanning direction by 3 dots, large dots are formed using the upper half nozzle. According to such an aspect, by printing each raster in two scans, it is possible to print by mixing large and small dots at the same ratio.
[0106]
According to the printing apparatus described above, the expected amount of ink for each color is determined in accordance with the input image data while keeping the ink duty limit, and the amount of ink discharged exceeds the expected value. Since the dot diameter is determined in such a range, it is possible to use various dots having different densities and dot diameters under the condition that the ink duty is always limited. In addition, there is an advantage that the best image quality can be obtained for the following reason.
[0107]
Dots with different dot diameters allow multi-tone expression, make the dot granularity inconspicuous, and prevent dot formation unevenness due to mechanical manufacturing errors of the printer 22 head, that is, banding. Can be used properly. For example, when dots with a large dot diameter appear to be concentrated in high density ink, the graininess becomes very noticeable. Appropriately mixed and used. Such a formation pattern for dots having different dot diameters may be a preferable pattern for each color, and there is little need to consider the influence of other colors or dot diameters.
[0108]
If the dot diameter is not set under the condition where the ink duty limit is satisfied in advance, the dot may not be formed with a preferable pattern as a result of the ink duty limit. According to the printing apparatus using the above-described means, it is possible to form dots having various dot diameters for each color in a preferable pattern based on the expected value of the ink discharge amount determined so as to keep the ink duty limit. Therefore, a good image can be formed.
[0109]
Further, the above-described means has the following advantages. When trying to increase the types of dots having different densities per unit area for a certain hue, there are a method of increasing the ink density and a method of increasing the dot diameter. In general, it is difficult to increase the types of ink density because it is necessary to newly install an ink cartridge and a head. However, it is relatively easy to increase the dot diameter to other types by increasing the types of drive waveforms described above. Can be realized. When the number of types of dot diameters is increased to further increase the number of gradations, according to the above-described means, the ink discharge amount determined by the correlation with other colors can be used as it is, and can be processed independently with ink for each color. This can be dealt with by slightly changing the dot diameter selection process. Therefore, the above-described means has an advantage that it is advantageous in terms of the possibility of further increasing the gradation expression of the printing apparatus once designed.
[0110]
Furthermore, since the printing apparatus includes processing by a computer, it is possible to adopt an embodiment as a recording medium in which a program for realizing each function described above is recorded. Such storage media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, ROM cartridges, punch cards, printed matter printed with codes such as barcodes, computer internal storage devices (such as RAM and ROM). A variety of computer-readable media can be used, such as memory) and external storage devices. Moreover, the aspect as a program supply apparatus which supplies the computer program which implement | achieves the function of each process or each means of said invention to a computer via a communication path is also possible.
[0111]
Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various embodiments can be implemented without departing from the spirit of the present invention. For example, although the various processes described above are executed by the computer 90, the printer 22 may be provided with a function for executing such processes and executed on the printer 22 side.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image processing system using a printer of the present invention.
FIG. 2 is a schematic configuration diagram of a printer of the present invention.
FIG. 3 is an explanatory diagram showing a schematic configuration of a dot recording head of a printer of the present invention.
FIG. 4 is an explanatory diagram illustrating a principle of dot formation in the printer of the present invention.
FIG. 5 is an explanatory diagram illustrating an example of nozzle arrangement in a printer.
FIG. 6 is an explanatory diagram showing nozzle arrangement in the printer of the present invention.
FIG. 7 is an explanatory diagram showing the principle of forming dots with different dot diameters according to the present invention.
FIG. 8 is an explanatory diagram showing a nozzle drive waveform and a state of dots formed by the drive waveform in the printer 22 of the present invention.
FIG. 9 is an explanatory diagram showing an internal configuration of the printer 22;
FIG. 10 is an explanatory diagram showing a drive circuit configuration of a head.
FIG. 11 is a flowchart showing the flow of a dot generation processing routine.
FIG. 12 is a flowchart showing a flow in a first mode of each color ejection ink amount determination processing routine;
FIG. 13 is an explanatory diagram illustrating a cyan ink amount table;
FIG. 14 is an explanatory diagram illustrating a light cyan ink amount table;
FIG. 15 is a flowchart showing a flow in a second mode of each color ejection ink amount determination processing routine;
FIG. 16 is an explanatory diagram showing a state of a grid of the ink amount table in the second mode.
FIG. 17 is a flowchart showing a flow in a first mode of a dot diameter setting processing routine.
FIG. 18 is an explanatory diagram showing a dot on / off determination method using a dither matrix.
FIG. 19 is a flowchart showing a flow in a second mode of the dot diameter setting processing routine.
FIG. 20 is an explanatory diagram showing weighting factors in error diffusion processing.
FIG. 21 is a flowchart showing a flow in a third mode of a dot diameter setting processing routine.
FIG. 22 is an explanatory diagram showing a table for giving ink amounts by dot diameter in the third mode.
FIG. 23 is an explanatory diagram showing an aspect in which large and small dots are mixedly recorded.
[Explanation of symbols]
12 ... Scanner
21 ... Color display
22 Color printer
23 ... Paper feed motor
24 ... Carriage motor
26 ... Platen
28 ... Print head
31 ... Carriage
32 ... Control panel
34 ... Sliding shaft
36 ... Drive belt
38 ... pulley
39 ... Position detection sensor
40 ... Control circuit
41 ... CPU
42 ... Programmable ROM (PROM)
43 ... RAM
44 ... PC interface
45 ... PIO
46 ... Timer
47 ... Transfer buffer
51 ... Transmitter
55 ... Distribution output device
61, 62, 63, 64, 65, 66... Ink ejection head
67 ... Introducing pipe
68 ... Ink passage
71 ... cartridge for black ink
72. Color ink cartridge
90 ... Personal computer
91 ... Video driver
92 ... Input section
95 ... Application program
96 ... Printer driver
97 ... Rasterizer
98 ... Expected ink amount setting module
99 ... Halftone module

Claims (9)

A printing apparatus capable of printing an image by forming a plurality of dots on a print medium,
Input means for inputting image data for each pixel constituting the image;
A head comprising two or more types of inks having different densities for at least one hue and capable of forming two or more types of dots having different ink amounts for each ink;
An ink amount expected value setting means for setting an expected value of the ink amount to be used for forming a dot for each pixel based on the image data for the inks having different densities;
Based on the set expected ink amount, each of the inks having different densities can be selected by selecting which of the two or more types of dots should be formed, including non-forming dots. Multi-value conversion means for performing value conversion;
Dot forming means for forming the selected dots,
The multi-value conversion means includes
Type-specific expected value setting means for setting a type-specific expected value for each type of dot that can be formed by the head based on the ink amount expected value determined by the ink amount expected value determining means When,
A printing apparatus, comprising: a multi-value quantization unit having a unit that determines whether or not dots are formed based on the set expected value for each type of dot using an error diffusion method. The printing apparatus according to claim 1,
The image data is data including a gradation value for at least one color component in a color space;
The ink amount expected value setting means includes:
Expected value storage means for storing the expected value of the ink amount as a table corresponding to combinations of gradation values of a plurality of color components in the color space;
A printing apparatus comprising: means for setting an expected value of the ink amount for each pixel by referring to a table stored in the expected value storage means based on input image data. The printing apparatus according to claim 2,
The table stored in the expected value storage means sets the expected value of the ink amount to the expected value of the ink amount of the other colors regardless of whether the hue is the same as the expected value of each ink to be set. A printing apparatus that is a table that stores values that are determined in relation to each other in correspondence with combinations of gradation values of a plurality of color components in the color space. The printing apparatus according to claim 1,
Two or more types of dots formed for the same hue by the head include two or more types of dots having an average density per unit area substantially equal when dots are formed at at least one recording density. . The printing apparatus according to any one of claims 1 to 4,
The ink amount expected value setting means is a range in which the total amount of ink used for forming dots per unit area does not exceed a predetermined amount determined according to the printing medium regardless of whether or not the hue is the same. A printing apparatus as means for setting an expected value of the ink amount. The printing apparatus according to claim 1,
The head is a printing apparatus provided with a mechanism for ejecting ink particles by pressure applied to ink by applying a voltage to an electrostrictive element provided in an ink passage. The printing apparatus according to claim 1,
The head is a printing apparatus provided with a mechanism for ejecting ink particles by pressure applied to ink in an ink passage by bubbles generated by energization of a heating element provided in the ink passage. Forming a plurality of dots on a print medium using a head that includes two or more types of inks having different densities for at least one hue and capable of forming two or more types of dots having different ink amounts for each ink. A printing method for printing an image by:
For each pixel that makes up the image, input the image data,
For the ink of different density, set an expected value of the amount of ink to be used for dot formation for each pixel based on the image data,
Based on the set expected ink amount, each of the inks having different densities can be selected by selecting which of the two or more types of dots should be formed, including non-forming dots. Valuation,
A printing method for forming the selected dots;
The multi-value conversion is
Based on the expected amount of ink determined by the expected amount of ink determining means, an expected value for each type, which is an expected value for the amount of ink for each type of dot that can be formed by the head, is set.
A printing method that is performed by using an error diffusion method to determine whether or not dots are formed on the basis of the set expected value for each type of dot. A recording medium in which a program for printing an image by forming a plurality of dots on a printing medium is recorded so as to be readable by a computer,
A function for setting an expected value of the amount of ink to be used for forming dots for each pixel based on image data for inks having different densities prepared for at least one hue;
Based on the set expected ink amount, each of the inks having different densities can be selected by selecting which of the two or more types of dots should be formed, including non-forming dots. A function to perform valuation,
A recording medium on which a program for realizing the function of forming the selected dots by a computer is recorded;
The multi-valued function is
A function for setting an expected value for each type, which is an expected value for the amount of ink for each type of dot that can be formed by the head, based on the expected value for the amount of ink determined by the expected amount of ink value determining means;
A recording medium including a function performed by determining the presence / absence of dot formation based on the set expected value for each type of dot using an error diffusion method.

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